1. Field of the Invention
The present invention relates to a copper-based metal polishing solution and a method for manufacturing a semiconductor device.
2. Description of the Related Art
Formation of a wiring layer is included in the process of manufacturing a semiconductor device, and an etch-back technique is employed for eliminating stepped portions from a surface of the wiring layer. The etch-back technique comprises the steps of forming grooves conforming with a pattern of the wiring layer in an insulating film covering a substrate of a semiconductor substrate, depositing a copper film on the insulating film including the trenches, polishing the copper film with a polishing solution, and selectively allowing the copper film to remain within the trenches to form a buried wiring layer.
It was customary in the past to use a polishing solution prepared by dispersing polishing abrasive grains such as a colloidal silica in pure water. In the conventional technique, the polishing solution is supplied into a polishing pad included in a polishing apparatus, and the copper film formed on the substrate surface is polished, with a predetermined load applied to the polishing pad. In the conventional technique, however, a mechanical polishing, which involves the polishing abrasive grains and the polishing pad, is simply applied to the copper film, with the result that the polishing rate was as low as only 10 nm/min.
Other types of polishing solutions for a copper film or a copper alloy film are disclosed in, for example, xe2x80x9cJ. Electrochem. Soc., Vol. 138, No. 11, 3460 (1991)xe2x80x9d, xe2x80x9cVMIC Conference, ISMIC-101/92/0156 (1992)xe2x80x9d and xe2x80x9cVMIC Conference, ISMIC-102/93/0205 (1993)xe2x80x9d. To be more specific, disclosed in these publications are polishing solutions each consisting of a slurry of an amine-based colloidal silica or a slurry containing K3Fe(CN)6, K4(CN)6, or Co(NO3)2. However, the polishing solution disclosed in any of these publications gives rise to the difficulty that there is no difference in the etching rate of the copper film between the immersing step and the polishing step. As a result, the copper wiring layer within the trench is further etched with the polishing solution when the wiring layer is brought into contact with the polishing solution after the etch-back step. It follows that the upper surface of the copper wiring layer within the trench is positioned lower than the upper surface of the insulating film. In other words, it is difficult to form the wiring layer flush with the insulating film, leading to an impaired surface smoothness. What should also be noted is that the copper wiring layer buried in this fashion in the insulating film exhibits a resistivity higher than that of the copper wiring layer buried in the insulating film such that the upper surface of the wiring layer is flush with the upper surface of the insulating film.
Japanese Patent Disclosure (Kokai) No. 7-233485 discloses an additional copper-based metal polishing solution prepared by adding at least one kind of an organic acid selected from the group consisting of aminoacetic acid and amidosulfuric acid, and an oxidizing agent to water. Where elemental copper or a copper alloy is immersed in the copper-based metal polishing solution disclosed in this publication, the etching rate of the copper or copper alloy is very low. However, where the copper or copper alloy is subjected to a polishing treatment with the particular polishing solution, the etching rate of the copper or copper alloy is several to scores of times as high as that in the case of the immersion in the polishing solution. To be more specific, if aminoacetic acid included in the polishing solution disclosed in the above-noted publication reacts with hydrated copper, a complex compound soluble in water is formed, as shown below:
Cu(H2O)42++2H2NCH2COOHxe2x86x92Cu(H2NCH2COOH)2+4H2O+2H+
It should be noted that copper does not react with a mixture of aminoacetic acid and water. The reaction given above proceeds in a direction denoted by the arrow, if an oxidizing agent, e.g., hydrogen peroxide, is added to the reaction system, resulting in an etching of copper. If, for example, a copper film is immersed in the polishing solution, an oxide film is formed on the surface of the copper film so as to suppress the etching (dissolving) of the copper film. On the other hand, if the copper film is polished with a polishing pad containing the polishing solution, the oxide film formed on the film surface is mechanically removed by the polishing pad so as to expose the pure copper to the surface. It follows that the copper film is rapidly polished chemically by the functions of the aminoacetic acid and hydrogen peroxide contained in the polishing solution. It should be noted in this connection that the copper or copper alloy film tends to be dissolved in the polishing solution to some extent during a short period immediately after the polishing treatment and before formation of an oxide film on the film surface.
The prior art exemplified above, i.e., Japanese Patent Disclosure No. 7-233485, also discloses a method for manufacturing a semiconductor device in which a buried wiring layer made of copper or a copper alloy is formed by an etch-back technique using the copper-based metal polishing solution described above.
An object of the present invention is to provide a copper-based metal polishing solution which does not dissolve at all a copper or copper alloy film immersed therein and which permits the copper or copper alloy film to be polished at a practical rate in the polishing step.
Another object is to provide a method for manufacturing a semiconductor device, in which at least one member selected from the group consisting of a trench and an opening is formed in an insulating film on a semiconductor substrate, a wiring material selected from the group consisting of elemental copper and a copper alloy deposited on the insulating film can be etched back within short time period to form a buried wiring layer whose surface is level with the surface of the insulating film.
According to a first aspect of the present invention, there is provided a copper-based metal polishing solution, comprising a water-soluble organic acid capable of reaction with copper to form a copper complex compound which is unlikely to be dissolved in water and has a mechanical strength lower than that of copper, polishing abrasive grains and water.
According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising the steps of:
forming at least one member selected from the group consisting of a trench and an opening, the groove and opening conforming in shape with a wiring layer, in an insulating film formed on a semiconductor substrate;
depositing a wiring material selected from the group consisting of elemental copper and a copper alloy on the insulating film having at least one of the trench and opening formed therein; and
polishing the deposited wiring material film until a surface of the insulating film is exposed by using a polishing solution comprising a water-soluble organic acid capable of reaction with copper to form a copper complex compound which is unlikely to be dissolved in water and has a mechanical strength lower than that of copper, polishing abrasive grains and water, thereby forming a buried wiring layer in the insulating film such that surfaces of the wiring layer and the insulating film are level with each other.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.